1. Field of the Invention
The present invention relates to a silicon-based luminescent substance which is used in optical interconnection for optical communication and in visible light sources. The present invention also relates to a method for forming the luminescent substance, and to a light-emitting device using the luminescent substance.
2. Description of the Related Art
Compound semiconductors of, for example, gallium arsenide are candidates for light-emitting devices formed on silicon substrates for optical interconnection. In the compound semiconductors, it is difficult to produce structures having low defects on the silicon substrates, and thus, the compound semiconductors exhibit poor thermal stability. Moreover, the compound semiconductors cannot be produced only by conventional production processes for silicon integrated circuits, and additional processes result in increased production costs. Accordingly, novel production technologies have been awaited to make silicon-based light-emitting structures using only conventional production processes for silicon integrated circuits.
Porous silicon formed by anodization is known as a silicon-based luminescent substance (L. T. Canham, Appl. Phys. Lett., Vol. 57, No. 10, Sep. 3, 1990, pp. 1046-1048). Porous silicon, however, exhibits low luminous efficiency and a long luminous decay lifetime on the order of microseconds (xcexcsec). Since the production process includes complicated electrochemical wet processing, the process cannot be easily applied to production of silicon integrated circuits. Moreover, the resulting porous silicon is fragile.
Accordingly, it is an object of the present invention to provide a luminescent substance which can be formed on a substrate using a production process for silicon integrated circuits, which exhibits high luminous efficiency and a short luminous decay lifetime on the order of nanoseconds.
It is another object of the present invention to provide a method for making the luminescent substance at reduced cost.
It is still another object of the present invention to provide a light-emitting device using the luminescent substance which is used as a visible light source.
In a first aspect of the present invention, a luminescent substance comprises silicon and nitrogen as major components, the luminescent substance has an amorphous structure, the silicon content of the luminescent substance is greater than the stoichiometric silicon content of Si3N4, and the luminous intensity of the luminescent substance has a maximum at approximately 2.2 eV.
In the luminescent substance, there are dense and fine structures which contributes to light emission at approximately 2.2 eV. Thus, the luminescent substance exhibits high luminous efficiency and a short luminous decay lifetime.
Preferably, in the luminescent substance, the silicon is dispersed in a microcrystalline state and/or an amorphous state.
In a second aspect of the present invention, a method for forming a luminescent substance on a substrate comprises preparing silane (SiH4) and ammonia (NH3) as source gasses, and forming the luminescent substance on the substrate by one of a reduced pressure chemical vapor deposition process and a chemical vapor deposition process at a gas flow ratio of SiH4/(SiH4+NH3) of at least 0.1 and at a deposition temperature of 600 to 1,400xc2x0 C. so that the luminescent substance comprises silicon and nitrogen as major components, has a silicon-enriched amorphous structure, and has a maximum luminous intensity at approximately 2.2 eV (hereinafter, this method is referred to as a first method).
In a third aspect of the present invention, a method for forming a luminescent substance on a substrate comprises preparing dichlorosilane (SiH2Cl2) and ammonia (NH3) as source gasses, and forming the luminescent substance on the substrate by one of a reduced pressure chemical vapor deposition process and a chemical vapor deposition process at a gas flow ratio of SiH2Cl2/(SiH2Cl2+NH3) of at least 0.1 and at a deposition temperature of 600 to 1,400xc2x0 C. so that the luminescent substance comprises silicon and nitrogen as major components, has a silicon-enriched amorphous structure, and has a maximum luminous intensity at approximately 2.2 eV (hereinafter, this method is referred to as a second method).
In a fourth aspect of the present invention, a method for forming a luminescent substance on a substrate comprises preparing trichlorosilane (SiHCl3) and ammonia (NH3) as source gasses, and forming the luminescent substance on the substrate by one of a reduced pressure chemical vapor deposition process and a chemical vapor deposition process at a gas flow ratio of SiHCl3/(SiHCl3+NH3) of at least 0.1 and at a deposition temperature of 600 to 1,400xc2x0 C. so that the luminescent substance comprises silicon and nitrogen as major components, has a silicon-enriched amorphous structure, and has a maximum luminous intensity at approximately 2.2 eV (hereinafter, this method is referred to as a third method).
Preferably, in the second to fourth aspects, the gas flow ratio lies in a range of 0.2 to 0.7, and the deposition temperature lies in a range of 700 to 1,200xc2x0 C.
According to the first to third methods, the luminescent substance can be readily formed using a conventional system, such as a reduced pressure chemical vapor deposition system or a chemical vapor deposition system, with reduced production costs.
In a fifth aspect of the present invention, a light emitting device comprises a substrate and a luminescent layer comprising a luminescent substance. The luminescent substance comprises silicon and nitrogen as major components and has an amorphous structure, the silicon content of the luminescent layer is greater than the stoichiometric silicon content of Si3N4, and the luminous intensity of the luminescent substance has a maximum at approximately 2.2 eV.
The light-emitting device having a high luminous intensity at approximately 2.2 eV is suitable for use with optical fibers in the fields of optical interconnection.